The present invention relates to squarylium compounds which can be used in the optical recording field, and to optical recording media using the same.
In recent years, development of a digital versatile disc-recordable (DVD-R) as a recordable optical recording medium having a higher recording density than that of a compact disc-recordable (CD-R) has been under going. Both of CD-R and DVD-R are similar to each other in that an organic dye is utilized therein as a recording material and are also similar to each other in a principle of recording and reproducing of a signal (information). Therefore, the organic dyes developed for CD-R can basically comply with the various requirements (light resistance, solubility, and thermal decomposition properties) for the recording material of DVD-R other than spectroscopic properties. However, an oscillation wavelength of a semiconductor laser, which is used for recording the signal to DVD-R or for reproducing the signal from DVD-R, is in the range of 600-700 nm, which is shorter than that of the semiconductor laser which is used for CD-R. Accordingly, the recording material utilized for DVD-R should have an absorbance end of a longer wavelength side shorter than that of CD-R when it exists in the form of a membrane. Therefore, the dyes developed for CD-R such as cyanine dyes, azaannulene dyes and indoaniline-metal chelate dyes (xe2x80x9cElectronics Related Dyesxe2x80x9d, CMC, 1998) can not be used as the recording material for DVD-R.
The present inventors have developed squarylium compounds having two different kinds of aromatic substituents in a molecule. Such squarylium compounds have a squaric acid skeleton at a center of the molecule and substituents comprising an aromatic compound on carbon atoms at two catercornered positions of the skeleton. Squarylium compounds having two same aromatic substituents are conveniently referred to as symmetric squarylium compounds (or symmetric squarylium dyes), whereas those having two different kinds of substituents are referred to as asymmetric squarylium compounds (or asymmetric squarylium dyes).
A squarylium compound known in the art wherein a metal atom is coordinated thereby forming a chelate structure is a symmetric squarylium compound having an aniline derivative represented by the formula (A) as an aromatic substituent (Chem. Ber. vol. 103, 3553-3562, 1970). 
However, this compound does not have a structure in which a plurality of squarylium compounds coordinate to one metal atom, and nitrogen atoms between the aromatic ring and the squaric acid skeleton are involved in coordination.
In addition, a known compound in which a plurality of squarylium analogues coordinate to one metal atom to form a chelate structure is a compound represented by the formula (B) (xe2x80x9cOXOCARBONSxe2x80x9d, ACADEMIC PRESS 1980, p. 210, edited by Robert West).
However, in this compound, the substituents on the squaric acid skeleton are changed from an oxygen atom to an sulfur atom, and nitrogen atoms between the aromatic ring and the squaric acid skeleton are involved in coordination. 
Further, a complex of a compound represented by the formula (C) and a metal is known as an example which has an atom involved in coordination as a substituent on the aromatic ring, and in which a plurality of squarylium compounds and one metal atom form a complex. This complex may be used, for example, for a near infrared-ray absorbing agent, a filter for a plasma display, and the like (JP-A 2000-159776). 
(wherein X and Xxe2x80x2 represent a group having active hydrogen, Y1 and Y2 represent an hydrogen atom, an alkylamino group, or the like, and k and kxe2x80x2 represent an integer of 1 to 4)
However, the above reference discloses specifically only a compound represented by the formula (D) as a squarylium compound corresponding to the formula (C). Further, no specific structure for the complex is shown therein. 
(wherein Z1-Z6 represent a hydrogen atom, an alkyl group, or the like)
Squarylium compounds having a structure in which a plurality of squarylium compounds coordinate to one metal atom, and in which atoms involved in coordination are an oxygen atom being a substituent on the squaric acid skeleton and an atom in a substituent on an aromatic ring, have not been known yet.
In view of an oscillation wavelength of the semiconductor laser used for DVD-R, for spectroscopic properties of the recording material, which have the close relation with recording and reproducing sensitivities of the signal, it is desirable that the maximum absorption wavelength (xcexmax) of the recording material measured in a solution state is within the range of 550-600 nm and log xcex5 (xcex5 is a molar extinction coefficient) at the maximum absorption wavelength is 5 or larger.
In addition, for thermal decomposition properties of the recording material, which have the close relation with the recording sensitivity, it is desirable that the recording material decomposes within the temperature range of 250-350xc2x0 C.
Furthermore, although light resistance and solubility in a solvent which is necessary for membrane formation are also required as the property of the recording material, when the known squarylium compounds are used in a recording material for DVD-R, the obtained recording material for DVD-R is not sufficient for practical use in view of spectroscopic properties, light resistance, solubility and thermal decomposition properties. The above-mentioned compound A has a melting point of 350xc2x0 C. or higher, and the compound C has a maximum absorption wavelength of 830 nm or longer. There are no property data for the compound B.
An object of the present invention is to provide squarylium compounds having spectroscopic properties, light resistance, solubility and thermal decomposition properties suitable for a recording material for DVD-R, and optical recording media using the same.
In view of the above situation, the present inventors intensively investigated and, as the result, we have found that a suqarylium compound having hydroxypyrazole as an aromatic substituent and a metal atom with a coordination ability form a chelate complex, and obtained a finding that compounds obtained by forming such a chelate complex have properties suitable for a recording material for DVD-R.
The present invention was done based on such a finding, and provides squarylium compounds represented by the formula (I): 
wherein, R1 and R2 are the same or different, and represent an alkyl group optionally having a substituent, an aralkyl group optionally having a substituent, an aryl group optionally having a substituent, or a heterocyclic group optionally having a substituent; Q represents a metal atom with a coordination ability; q represents 2 or 3; and A represents an aryl group optionally having a substituent, a heterocyclic group optionally having a substituent, or Yxe2x95x90CHxe2x80x94 wherein Y represents an aryl group optionally having a substituent or a heterocyclic group optionally having a substituent, and optical recording media which has a recording layer comprising said squarylium compound.
The present invention will be illustrated below, and herein the compound represented by the formula (I) is referred to as a compound (I). This is also applicable to compounds with other formula numbers added.
First, in the definitions of the respective groups in the above formula (I) or the formula (II) described below, an alkyl part of the alkyl and alkoxy groups includes straight or branched alkyl groups having from 1 to 6 carbon atoms and cyclic alkyl groups having from 3 to 8 carbon atoms, such as methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, tert-butyl, pentyl, iso-pentyl, 1-methylbutyl, 2-methylbutyl, tert-pentyl, hexyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl groups, and the like.
Examples of the aralkyl group include aralkyl groups having from 7 to 15 carbon atoms, such as benzyl, phenethyl, phenylpropyl and naphthylmethyl groups, and the like.
Examples of the aryl group include phenyl, naphthyl, anthryl and azulenyl groups, and the like.
The halogen atom includes chlorine, bromine, fluorine and iodine atoms.
The substituents for the aralkyl group, the aryl group, the alkoxy group, the aromatic ring, the heterocyclic ring or the heterocyclic group are the same or different 1 to subtutituents, and include a hydroxyl group, a carboxyl group, a halogen atom, an alkyl group optionally having a substituent, an alkoxy group, a nitro group, an amino group optionally having a substituent, and the like, wherein the halogen atom, the alkyl group and the alkoxy group include those as described above.
The substituents for the alkyl group are the same or different 1 to 3 substituents, and include a hydroxyl group, a carboxyl group, a halogen atom, an alkoxy group, and the like, wherein the halogen atom and the alkoxy group include those as described above. Further, the substituents for the alkyl group include substituents for the alkyl group as described below.
The substituents for the amino group are the same or different 1 or 2 alkyl groups, wherein the alkyl group includes those as described above.
Examples of the metal atom with a coordination ability include aluminium, zinc, copper, iron, nickel, chromium, cobalt, manganese, iridium, vanadium, titanium, and the like. Among them, preferred are trivalent metals (e.g., aluminium, iron (III), chromium (III), cobalt (III), manganese (III), iridium (III), vanadium (II), and the like). Aluminium is more preferable.
The aromatic ring which is formed by two adjacent R6s being taken together with two adjacent carbon atoms includes a benzene ring, a naphthalene ring, an anthracene ring, and the like.
The heterocycle in the heterocyclic group or the heterocycle which is formed by R3 and R4 being taken together with an adjacent carbon atom includes 5- or 6-membered monocyclic aromatic or aliphatic heterocycles containing at least one atom selected from nitrogen, oxygen and sulfur atoms, fused di- or tri-cyclic aromatic heterocycles, which are formed by fusing 3- to 8-membered rings and which contain at least one atom selected from nitrogen, oxygen and sulfuir atoms, and the like, and, more particularly, includes pyridine, pyrazine, pyrimidine, pyridazine, quinoline, isoquinoline, phthalazine, quinazoline, quinoxaline, naphthyridine, cinnoline, pyrrole, pyrazole, imidazole, triazole, tetrazole, thiophene, furan, thiazole, oxazole, indole, isoindole, indazole, benzimidazole, benzotriazole, benzothiazole, benzoxazole, purine, carbazole, pyrrolidine, piperidine, piperazine, morpholine, thiomorpholine, homopiperidine, homopiperazine, tetrahydropyridine, tetrahydroquinoline, tetrahydroisoquinoline, tetrahydrofuran, tetrahydropyran, dihydrobenzofuran, tetrahydrocarbazole, indoline rings, and the like.
Examples of the alicyclic hydrocarbon ring which is formed by R3 and R4 being taken together with an adjacent carbon atom include saturated or unsaturated alicyclic hydrocarbon rings having from 3 to 8 carbon atoms, such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclopentene, 1,3-cyclopentadiene, cyclohexene and cyclohexadiene rings, and the like.
In the compound (I), a compound wherein Y is an indoline ring optionally having a substituent is preferred, and, among them, more preferred is a compound wherein Yxe2x95x90CHxe2x80x94 is represented by the general formula (II): 
wherein R3 and R4 are the same or different, and represent an alkyl group optionally having a substituent, or R3 and R4 may be taken together with an adjacent carbon atom to form an alicyclic hydrocarbon ring or a heterocycle optionally having a substituent; R5 represents a hydrogen atom, an alkyl group optionally having a substituent, an aralkyl group optionally having a substituent or an aryl group optionally having a substituent; R6 represents a halogen atom, an alkyl group optionally having a substituent, an aralkyl group optionally having a substituent, an aryl group optionally having a substituent, a nitro group, a cyano group or an alkoxy group optionally having a substituent; and n represents an integer of 0-4, and when n is 2-4, then R6s are the same or different, or two adjacent R6s may be taken together with two adjacent carbon atoms to form an aromatic ring optionally having a substituent.
A general method for preparing the compound (I) is explained below. 
(wherein R1, R2, A, Q and q are the same as defined above, and Y represents a hydrogen atom, potassium, sodium, or the like)
The compound (V) is prepared by reacting the compound (III) with 0.7- to 1.5-fold moles of the compound (IV) at 0-80xc2x0 C. for 5 minutes to 15 hours in a solvent, if needed, in the presence of a base.
Examples of the base to be used include inorganic bases such as potassium carbonate, sodium carbonate, potassium hydroxide and the like, and organic bases such as triethylamine, sodium methoxide, and the like, and so on. A preferred amount of the base to be used is 0.7- to 1.5-fold moles relative to the compound (III).
Examples of the solvent to be used include methanol, ethanol, dimethylformamide, and the like.
The compound (VI) is prepared by treating the compound (V) at 0-80xc2x0 C. for 30 minutes to 15 hours in an alkaline solvent or in an acidic solvent.
Examples of the alkaline solvent to be used include an aqueous potassium carbonate solution an aqueous sodium carbonate solution, an aqueous potassium hydroxide solution, and the like.
Examples of the acidic solvent to be used include a 50 volume/volume % solution of hydrochloric acid in aqueous dimethyl sulfoxide, a 50 volume/volume % solution of hydrochloric acid in aqueous dimethylformamide, and the like.
The compound (VII) is prepared by reacting the compound (VI) with 0.5- to 2-fold moles of A-H at 50-120xc2x0 C. for 5 minutes to 15 hours in a solvent, if needed, in the presence of 0. 5- to 2-fold moles of a base.
Examples of the solvent to be used include alcoholic solvents alone having from 2 to 8 carbon atoms such as ethanol, propanol, iso-propyl alcohol, butanol, octanol, and the like, and a mixture of the alcoholic solvent with benzene, toluene or xylene (50 volume/volume % or more of the alcoholic solvent is preferable).
Examples of the base to be used include organic bases such as quinoline, triethylamine, pyridine, and the like, and inorganic bases such as potassium carbonate, potassium hydrogen carbonate, sodium hydrogen carbonate, and the like, and so on.
The compound (I) is prepared by reacting the compound (VII) with a material providing Qq+ at room temperature to 120xc2x0 C. for 5 minutes to 15 hours in a solvent, if needed, in the presence of 0.5- to 2-fold moles of acetic acid. It is preferred that the material providing Qq+ is used so that the ratio of the mole number of the compound (VII): (the mole number of the material providing Qq+)xc3x97q is 1:0.5-2.
Examples of the material providing Qq+ to be used include aluminium tris(acetylacetonate), aluminum tris(ethylacetoacetate), aluminum isopropoxide, aluminium sec-butoxide, aluminium ethoxide, aluminium chloride, copper chloride, copper acetate, nickel acetate, and the like.
Examples of the solvent to be used include halogen solvents such as chloroform, dichloromethane, and the like; aromatic solvents such as toluene, xylene, and the like; ethers such as tetrahydrofuran, methyl tert-butyl ether and the like; esters such as ethyl acetate, and the like, and so on.
Embodiments of the compound (I) are shown in Table 1. Additionally, the compound numbers in the table correspond to the Example numbers described below. Further, in the table, xe2x80x9cPhxe2x80x9d represents a phenyl group, xe2x80x9cMexe2x80x9d represents a methyl group, xe2x80x9cPrxe2x80x9d represents a propyl group, and xe2x80x9ciPrxe2x80x9d represents an isopropyl group.
Next, the constitution of a recording medium utilizing the squarylium compound of the present invention (hereinafter, it may be referred to as xe2x80x9ca compound of the present inventionxe2x80x9d) will be illustrated.
The physical properties required for a material for a recording layer include optical and thermal properties, as well as light resistance.
The optical properties are preferably such that there is a large absorption band at a shorter wavelength side than 600-700 nm, preferably 630-690 nm, which is a recording or reproducing wavelength of DVD-R or the like, and, further a recording or reproducing wavelength is in the vicinity of a longer wavelength end of the above-mentioned absorption band. This means that the above-mentioned material for the recording layer has a larger refractive index and extinction coefficient within 600-700 nm, which is a recording or reproducing wavelength.
More specifically, the refractive index xe2x80x9cnxe2x80x9d of a single layer of the recording layer is preferably 1.5-3.0, and the extinction coefficient xe2x80x9ckxe2x80x9d of a single layer of the recording layer is preferably within the range of 0.02-0.3, for the light of the wavelength range of the recording or reproducing wavelengthxc2x15 nm in the vicinity of the longer wavelength end of the above-mentioned absorption band. When xe2x80x9cnxe2x80x9d is 1.5 or larger, a reflectance and a modulation percentage of recording become higher, and when xe2x80x9cnxe2x80x9d is 3.0 or smaller, an error does not occur with the light in the recording or reproducing wavelength range. In addition, when xe2x80x9ckxe2x80x9d is 0.02 or larger, the recording sensitivity is improved, and when xe2x80x9ckxe2x80x9d is 0.3 or smaller, the reflectance of 50% or larger can be easily obtained.
In addition, the maximum absorption wavelength (xcexmax) of the material for the recording layer which is measured in a chloroform solution is preferably within the range of 550-600 nm, and since a larger extinction coefficient allows for the larger refractive index xe2x80x9cnxe2x80x9d, log xcex5 (xcex5 is a molar extinction coefficient) at the maximum absorption wavelength is preferably 5 or larger.
Further, for the thermal properties, it is preferred that the decomposition temperature is within the particular temperature range. More specifically, the decomposition temperature is preferably 350xc2x0 C. or lower, and more preferably within the range of 250-350xc2x0 C. When the decomposition temperature is 350xc2x0 C. or lower, it is not necessary to raise the power of the recording laser beam, and when it is 250xc2x0 C. or higher, it is preferable in a recording stability sense.
Still further, for the light resistance, it is preferred that the material has a reproducing property constant for over 1,000,000 repeats and a fastness property in which no color fading occurs when the material is left in a room.
The preferable substrate shape is under the condition that a track pitch is within the range of 0.7-0.8 xcexcm and a groove width at the half band width is within the range of 0.18-0.40 xcexcm.
It is preferred that the substrate has a guiding groove having a depth of 1,000-2,500 xc3x85. It is preferred that the track pitch is 0.7-1.0 xcexcm, and more preferably 0.7-0.8 xcexcm for the high recording density application. The groove width is preferably 0.18-0.40 xcexcm as the half band width. When the groove width is 0.18 xcexcm or wider, the adequate strength of a tracking error signal can be easily detected, whereas when it is 0.40 xcexcm or narrower, the recording portion is hardly widened in a traverse direction upon recording, being preferable.
1. The Structure of an Optical Recording Medium
The optical recording medium of the present invention may be formed into an air-sandwich structure or into a closely adhered structure which is applied to general recordable discs, or may be formed into a structure of a recordable optical recording medium such as DVD-R, or the like.
2. The Required Properties and Embodiments of Constituent Materials for Each Layer
The optical recording medium of the present invention has a basic structure in which a first substrate and a second substrate are adhered via a recording layer with an adhesive. The recording layer may be a single layer of an organic dye layer comprising the compound of the present invention, or may be a laminated layer of the organic dye layer and a metal reflective layer for enhancing the reflectance. Between the recording layer and the substrate, an undercoat layer or a protective layer may be built-up, or they may be laminated for improving the function. Preferred structures include the first substrate/the organic dye layer/the metal reflective layer/the protective layer/the adhesive layer/the second substrate and the like.
a. Substrate
The substrate to be used should be transmittable to the wavelength of the laser beam to be used when recording or reproducing is conducted from a substrate side, but it is not necessary for the substrate to be transmittable to the wavelength when recording or reproducing is conducted from a recording layer side. As the material for the substrate, for example, plastics such as polyester, acrylic resin, polyamide, polycarbonate resin, polyolefin resin, phenolic resin, epoxy resin, polyimide, or the like, glasses, ceramics, metals or the like may be used. Additionally, a guiding groove or a guiding pit for tracking, a preformat such as an addressing signal, or the like may be formed on a surface of the substrate.
b. Recording Layer
The recording layer is a layer in which some optical change is caused by irradiation with a laser beam and, thereby, an information is recorded, and should contain the compound of the present invention. The compounds of the present invention may be used alone or in combination of two or more for forming the recording layer.
In addition, the compound of the present invention may be used by mixing it or laminating it with other organic dyes, metals or metal compounds for the purpose of enhancement of the optical properties, the recording sensitivity, the signal properties, or the like. Examples of the organic dye include a polymethine dye, naphthalocyanine, phthalocyanine, squarylium, croconium, pyrylium, naphthoquinone, anthraquinone (indanthrene), xanthene, triphenylmethane, azulene, tetrahydrocholine, phenanthrene and triphenothiazine dyes, metal complex compounds, and the like. Examples of the metal and metal compound include In, Te, Bi, Se, Sb, Ge, Sn, Al, Be, TeO2, SnO, As, Cd, and the like, each of which may be used in the form of dispersion mixture or lamination.
In addition, it is possible to enhance the light resistance significantly by mixing a light stabilizer into the compound of the present invention. As the light stabilizer, metal complexes and aromatic amines are preferable. Embodiments of the light stabilizer will be listed below (see Tables 2 and 3).
The mixing ratio of the light stabilizer relative to the compound of the present invention is preferably 5-40% by weight. When the ratio is 5% by weight or larger, the effect on light stabilization is high, and it is preferred that the ratio is 40% by weight or smaller in view of the recording or reproducing properties.
In addition, macromolecular materials, for example, various materials such as ionomer resin, polyamide resin, vinyl resin, natural polymer, silicone or liquid rubber, or silane coupling agents may be dispersed and mixed into the compound of the present invention, and additives such as stabilizers (for example, transition metal complex), dispersing agents, flame retardants, lubricants, antistatic agents, surfactants or plasticizers may be used together for the purpose of modifying the properties.
The recording layer may be formed using conventional methods such as a deposition, a sputtering, a chemical vapor deposition or a solvent coating. In the case where the coating method is used, the dye comprising the compound of the present invention with the aforementioned additives added optionally is dissolved in an organic solvent, and the solution is coated by the conventional coating method such as a spraying, a roller coating, a dipping or a spin coating.
Examples of the organic solvent to be used generally include alcohols such as methanol, ethanol and iso-propanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N,N-dimethylformamide and N,N-dimethylacetoamide, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydroftiran, dioxane, diethyl ether and ethyleneglycol monomethyl ether, esters such as methyl acetate and ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethane, carbon tetrachloride and trichloroethane, aromatic compounds such as benzene, xylene, monochlorobenzene and dichlorobenzene, cellosolves such as methoxyethanol and ethoxyethanol, and hydrocarbons such as hexane, pentane, cyclohexane and methylcyclohexane.
The membrane thickness of the recording layer is preferably 100 xc3x85-10 xcexcm, more preferably 200-2,000 xc3x85.
Embodiments of the light stabilizer to be used in combination with the compound of the present invention are listed below.
(1) Metal Complex-light Stabilizers (See Table 2) 
wherein Ra and Rb are the same or different, and represent a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, wherein said alkyl group, said aryl group or said heterocyclic group may have a substituent. 
wherein Ra, Rb, Rc and Rd are the same or different, and represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cyclic alkyl group or a heterocyclic group, wherein said alkyl group, said aryl group, said cyclic alkyl group or said heterocyclic group is bound directly or indirectly via a divalent linking group. 
wherein X represents O, S or CRaRb, wherein Ra and Rb are the same or different, and represent CN, CORc, COORd, CONReRf, SO2Rg, or a group of atoms necessary for forming a 5- or 6-membered ring, and wherein Rcxcx9cRg are the same or different, and represent an alkyl group or an aryl group, wherein said alkyl group or said aryl group may have a substituent. 
wherein Ra, Rb, Rc and Rd are the same or different, and represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cyclic alkyl group or a heterocyclic group, wherein said alkyl group, said aryl group, said cyclic alkyl group or said heterocyclic group is bound directly or indirectly via a divalent linking group, and Re represents a hydrogen atom, an alkyl group, an aryl group, an acyl group, a carboxyl group, an alkoxycarbonylalkyl group or a sulfo group. 
wherein Ra, Rb, Rc and Rd are the same or different, and represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cyclic alkyl group or a heterocyclic group, wherein said alkyl group, said aryl group, said cyclic alkyl group or said heterocyclic group is bound directly or indirectly via a divalent linking group, and Re and Rf are the same or different, and represent a hydrogen atom, an alkyl group, an aryl group, an acyl group, a carboxyl group or a sulfo group. 
wherein X represents O or S, Ra, Rb and Re are the same or different, and represent an alkyl group, an aryl group or a cyclic alkyl group, wherein said alkyl group, said aryl group or said cyclic alkyl group may have a substituent which is bound directly or via an oxy group, a thio group or an amino group, and the symbol: CCC represents Cxe2x95x90Cxe2x80x94C or Cxe2x80x94Cxe2x95x90C. 
wherein X represents O or S, Ra, Rb and Rc are the same or different, and represent an alkyl group an aryl group or a cyclic alkyl group, wherein said alkyl group, said aryl group or said cyclic alkyl group may have a substituent which is bound directly or via an oxy group, a thio group or an amino group, Rb represents an alkyl group or an aryl group, and the symbol: CCC represents Cxe2x95x90Cxe2x80x94C or Cxe2x80x94Cxe2x95x90C. 
wherein Ra and Rb are the same or different, and represent a hydrogen atom, an alkyl group, an aryl group or a heterocyclic group, wherein said alkyl group, said aryl group or said heterocyclic group may have a substituent. 
wherein Ra Rb, Rc and Rd are the same or different, and represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cyclic alkyl group or a heterocyclic group, wherein said alkyl group, said aryl group, said cyclic alkyl group or said heterocyclic group is bound directly or indirectly via a divalent linking group. 
wherein Ra, Rb, Rc and Rd are the same or different, and represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group, a cyclic alkyl group or a heterocyclic group, wherein said alkyl group, said aryl group or said cyclic alkyl group is bound directly or indirectly via a divalent linking group, Re represents a hydrogen atom, an alkyl group, an aryl group, an acyl group, a carboxyl group or a sulfo group.
In the formulae (A)-(J), M represents a transition metal such as Ni, Pd, Pt, Cu, Co, or the like, and may have a charge to form a salt with a cation, and in addition, other ligands may be bonded above or below M. Such salts may be used also as a light stabilizer. The alkyl, cyclic alkyl, aryl and heterocyclic groups and substituents therefor include those described above.
More preferable embodiments are shown in Table 2.
(2) Aromatic Amine-light Stabilizers (See Table 3)
Following compounds may be used. 
wherein Rg, Rh, Ri and Rj are the same or different, and each represents a hydrogen atom, or an alkyl group optionally having a substituent, X represents an acid anion, and G is, when m is 1 or 2, 
wherein p is 1 or 2, and is, when m is 2, 
wherein all of existing aromatic rings may be substituted with an alkyl group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 6 carbon atoms, a halogen atom or a hydroxyl group.
More preferred embodiments are shown in Table 3.

c. Undercoat Layer
The undercoat layer is used for the purpose of (1) an improvement in adherability, (2) a barrier against water, gases, or the like, (3) an improvement in the tability of the recording layer, (4) an enhancement of the reflectance, (5) a protection of the substrate from a solvent, (6) a formation of a guiding groove, guiding pit or preformat, or the like. With regard to the purpose of (1), macromolecular materials, for example, various polymers such as ionomer resin, polyamide resin, vinyl resin, natural resin, natural polymer, silicone, liquid rubber, or the like, silane coupling agents, or the like may be used. With regard to the purposes of (2) and (3), in addition to the aforementioned macromolecular materials, inorganic compounds such as SiO, MgF, SiO2, TiO, ZnO, TiN, SiN, or the like, and further metals or semimetals such as Zn, Cu, Ni, Cr, Ge, Se, Au, Ag, Al, or the like may be used. In addition, with regard to the purpose of (4), metals such as Al, Au, Ag, or the like, or organic films having metallic luster such as a methine dye, a xanthene dye, or the like may be used. With regard to the purposes of (5) and (6), a ultraviolet-curing resin, a thermosetting resin, a thermoplastic resin, or the like may be used.
The membrane thickness of the undercoat layer is preferably 0.01-30 xcexcm, more preferably 0.05-10 xcexcm.
d. Metal Reflective Layer
Examples of the material for the metal reflective layer include poorly erodable metals, semimetals, and the like exhibiting a high reflectance themselves. Embodiments of the material for the metal reflective layer include Au, Ag, Cr, Ni, Al, Fe, Sn, and the like, but Au, Ag and Al are most preferred from a viewpoint of the reflectance and productivity. These metals or semimetals may be used alone or as an alloy of two of them.
The method for forming a membrane includes a vapor deposition, a sputtering, and the like. The membrane thickness of the metal reflective layer is preferably 50-5,000 xc3x85, more preferably 100-3,000 xc3x85.
e. Protective Layer, Substrate Surface-hard Coating Layer
A protective layer and a substrate surface-hard coating layer are used for the purpose of (1) a protection of the recording layer (reflection absorbing layer) from flaw, dust, dirt or the like, (2) an improvement in the storage stability of the recording layer (reflection absorbing layer), (3) an improvement in the reflectance, or the like. With regard to such purposes, the materials described for the undercoat layer may be used. In addition, SiO, SiO2 or the like may be used as an inorganic material, and thermo-soflening resins such as polymethyl acrylate, polycarbonate, polystyrene, polyester, vinyl resin, cellulose, aliphatic hydrocarbons, natural rubber, styrene-butadiene, chloroprene rubber, wax, alkyd, drying oil, or rosin, thermosetting resins such as epoxy resin, phenol resin, polyurethane resin, melamine resin, or urea resin, ultraviolet-curing resins such as polyester acrylate, epoxy acrylate, urethane acrylate, or silicone acrylate, or the like may be used as an organic material, but among them, the ultraviolet-curing resins may be preferably used in that they have the excellent productivity.
The membrane thickness of the protective layer or the substrate surface-hard coating layer is preferably 0.01-30 xcexcm, more preferably 0.05-10 xcexcm. In the present invention, stabilizers, dispersing agents, flame retardants, lubricants, antistatic agents, surfactants, plasticizers or the like may be incorporated into the above undercoat layer, protective layer and substrate surface-hard coating layer as described for the recording layer.
f. Protective Substrate
A protective substrate should be transmittable to the wavelength of the laser beam to be used when the laser beam is irradiated from this protective substrate side, whereas it may be transmittable or not to the wavelength when it is used as a mere protective plate. The materials which may be used for the protective substrate are the same as those for the substrate, and plastics such as polyester, acrylic resin, polyamide, polycarbonate resin, polyolefin resin, phenol resin, epoxy resin, or polyimide, or the like, glasses, ceramics, metals, or the like may be used.
g. Adhesive, Adhesive Layer
As the adhesive, any material which can adhere two recording media may be used, but from a viewpoint of the productivity, ultraviolet-curing or hot melt adhesives are preferred.